We have collected one-dimensional raster-scan observations of the active star-forming region Sharpless 171 (S171), a typical HII region-molecular cloud complex, with the three spectrometers (LWS, SWS, and PHT-S) on board ISO. We have detected 8 far-infrared fine-structure lines, [] 52 μm, [] 57 μm, [] 63 μm, [] 88 μm, [] 122 μm, [] 146 μm, [] 158 μm, and [] 35 μm together with the far-infrared continuum and the H2 pure rotation transition (–3) line at 9.66 μm. The physical properties of each of the three phases detected, highly-ionized, lowly-ionized and neutral, are investigated through the far-infrared line and continuum emission. Toward the molecular region, strong [] 146 μm emission was observed and the [] 63 μm to 146 μm line ratio was found to be too small (∼5) compared to the values predicted by current photodissociation region (PDR) models. We examine possible mechanisms to account for the small line ratio and conclude that the absorption of the [] 63 μm and the [] 158 μm emission by overlapping PDRs along the line of sight can account for the observations and that the [] 146 μm emission is the best diagnostic line for PDRs. We propose a method to estimate the effect of overlapping clouds using the far-infrared continuum intensity and derive the physical properties of the PDR. The [] 35 μm emission is quite strong at almost all the observed positions. The correlation with [] 122 μm suggests that the [] emission originates mostly from the ionized gas. The [] 35 μm to [] 122 μm ratio indicates that silicon of 30% of the solar abundance must be in the diffuse ionized gas, suggesting that efficient dust destruction is undergoing in the ionized region.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the UK) and with the participation of ISAS and NASA.

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.